The present invention relates to a grinder for use in a grinding apparatus which grinds foods, organic materials, minerals, or the like, into fine particles several to more than ten microns, in which a pair of grinding discs possess different strengths.
In a conventional grinder of a grinding apparatus, rotary and stationary discs are composed of the same whetstone having a low hardness. However, in this case, the rotary disc is worn away several times quicker than the stationary disc. Hence, the balance between the wearing speeds of the rotary and the stationary discs is quite bad, and the life of the discs is short. In addition, as the discs are worn away, the clearance between the rotary and the stationary discs is enlarged, and the particle size of the grinded material increases gradually with the result of lowering the accuracy of the grinded particles. Further, in this case, the whetstone particles worn away are mixed with the grinded material, which not only causes the contamination of the grinded material but lowers the purity of the same.
In the conventional grinder of the grinding apparatus, a rotary disc is secured to a rotary shaft arranged in the lower side of a housing and a stationary disc is mounted to a cover which is pivotally mounted to the top of the housing. Hence, in case of conducting an open or closed operation of the cover for carrying out the cleanup of the inside of the apparatus, a delicate disorder between the upper and the lower discs is liable to happen, and in order to properly perform the grinding of the material, the clearance adjustement between the two discs should be effected when the cover is opened and closed. This adjustment is troublesome and disadvantageous, and further it is quite difficult to maintain the grinding surfaces of the discs to a certain accuracy for a long time, which is a disadvantage. Further, when the grinding efficiency is lowered due to the wear and tear of the rotary and the stationary discs, the cover is disengaged and the two discs are replaced by new ones. Then, the grinding clearance between the upper and the loer discs must be adjusted again by a skilled operator, which considerably lowers the operational efficiency.